Three Democratic candidates for mayor were united in support for significant alterations to a multi-billion-dollar Alcosan proposal to deal with the region’s storm and wastewater runoff problem.

At a forum Wednesday night focused on environmental issues, city Councilman Bill Peduto noted that he and Allegheny County Executive Rich Fitzgerald had already called for changes in the plan to take advantage of “green” techniques to contain runoff closer to its sources by using features such as wetlands. Some environmental voices have criticized the plan, mandated by a federal consent decree, to make a massive investment in structures, including massive storage tunnels, designed to staunch the recurrent flows of untreated wastewater into rivers and streams.

“I want the city of Pittsburgh to be the model for all the other Alcosan communities,” Mr. Peduto said, maintaining that the incorporation of more green features could actually save on infrastructure costs.

Another candidate, Jack Wagner, the former state auditor general, denounced “this crazy tunnel proposal,” saying more should be done to separate storm and wastewater runoff at homes and other sites. State Rep. Jake Wheatley, D-Hill District, who’s also running for mayor, seconded the community-focused approach, saying that the city could encourage steps such as the widespread use of rain barrels in every neighborhoods.